Picture of How to dice an onion
This is the simplest and quickest way to dice an onion. If you don't want to cry--just breathe through your mouth the entire time. If you don't breathe through your nose you should be fine.

**Disclaimer 1: This project involves sharp knives. If your knife is dull, you have a tendency to chop off your appendages, or you are small child, you should not attempt this project.**

**Disclaimer 2: If you don't follow the breathing instructions, and this makes you cry, make sure you wash your hands before rubbing your eyes...then find a shoulder to cry on...**

Step 1: Slice off the top

Picture of Slice off the top
Slice off the top of the onion--do not cut off the root end!
u2beal9997 years ago
Yes, in culinary school and in commercial kitchens, you always start by cutting the onion in half through the root, peel, then cut the majority of the root "hairs" while leaving the root intact. This makes for a cleaner work area. Also, by cutting the onion in half, the cut side can lay flat on the board. This allows you to put pressure, with a flat palm, on the top of the onion while making the initial horizontal slices. This way even if the knife slips you aren't in danger of cutting yourself because the blade is lower than your hand and facing away from the body.
gglockner7 years ago
Noooo! The onion is round, and you are making cuts towards your hand. This technique landed me in the hospital for five stitches. There IS a better way -- quarter the onion first, then you can keep the onion on flat sides for all the cuts. Much safer, and really no more work. I'll try to upload my own instructions when I get a chance. Thx.
dizzydave (author)  gglockner7 years ago
your quartering method sounds safer...i'll give it a shot next time...
Great instructions, and the comments are helpful too! I tend to do this near running water, and put the onion under the faucet from time to time when the fumes get too bad and I can't see.

I'm still getting used to the posting here, so forgive me if this isn't the place. I'll try to do an instructable on this at some stage. I wrote a short guide on choosing the right kind of knife. As the author points out, it's important to have a good sharp one.

Choosing A Cooking Knife

dizzydave (author)  Sir Chopsalot7 years ago
if you breathe through your mouth the entire time you're usually ok--but if you get that one whiff through your nose you're toast.
I cut it in half before I even take the skin off. I find it is easier to remove the skin and as previously mentioned the cut side prevents the onion from rolling about while cutting.
dizzydave (author)  RebelWithoutASauce8 years ago
I have taken to doing this as well...if I wasn't lazy I'd redo the instructable...
lemonie8 years ago
Not quite the classical technique, but modified as jtobako suggests by cutting in half exactly what I use.
You cannot appreciate how worthwhile this method is unless you've seen (or tried) mangling an onion in other ways (I have seen such, it amused me)

jtobako8 years ago
Cut the onion in half and do half at a time. That way, the onion won't roll your fingers into the knife blade : ) If you are horrified by slicing into the root, cut it off center or just a slice off one side for a sturdy base. After cutting the onion, rub your hands with something stainless steel under running water-it will get rid of the onion smell.
dizzydave (author)  jtobako8 years ago
hmm...that's a great idea! i've known lot's of people who do this trick, but no one ever cuts it in half...